The invention relates to a folding rear-view mirror for motor vehicles consisting of a base tightly seated on the motor vehicle, a mirror unit capable of swiveling relative to the latter about an axis and a pivot drive unit composed of a motor and a drive gear. The invention relates in particular to external rear-view mirrors which under the control of an electric motor are not only adjustable from the interior of the vehicle but can also be swiveled inwards when driving through a car wash for instance. The swivel axis is substantially vertical so that the surface of the mirror is aligned roughly parallel to the side wall of the vehicle when the mirror is swiveled inwards.
In the operating position the mirror unit must remain exactly in position, even against air resistance during fast driving. For this reason it is held by a form-locking, usually spring-loaded positioning device and the drive must be self-locking when external forces act on the mirror unit. That means friction losses. When the entire mirror unit is swiveled inwards these forces must be overcome, which requires a considerable driving torque. This requires a powerful and, therefore, large motor and/or a very high transmission ratio in the drive gear when then also generates the self-locking at the expense of friction losses. The friction losses further increase the motor power required and reduce service life.
However the design is effected the construction space for the entire pivot drive unit is considerable. Regardless of how the pivot drive unit is accommodated in the base or in the mirror unit construction space is very scarce. Accordingly, the drive unit should be of the smallest possible size.
EP 644 084 P discloses a rear-view mirror in accordance with the generic category whose pivot drive unit consists of an electric motor and a transmission gear both of which are accommodated in the mirror unit. The transmission gear possesses two worm stages and two spur wheel stages in order to attain the required transmission ratio and degree of self-locking. It accordingly needs a relatively large construction space, especially to the side of the swivel axis and under the electric motor, which has a detrimental effect on the shape of the mirror unit and fouls the adjustment drive of the mirror. It is further disadvantageous that the worm stages generate high axial forces which must be transmitted into the housing and suffer from high wear with great frictional losses despite the structural parts being made of metal.
Accordingly, the aim of the invention is to construct and arrange the pivot drive unit in such a way that with an overall minimal requirement for space and a favorable assembled shape minimum frictional losses and high operational reliability are attained while production is simple.
According to the invention this achieved as follows by the characterizing characteristics of the first claim.
(a) Very large transmission ratios in the smallest construction space and with only small frictional losses may be achieved with a strain-wave gear which nevertheless is self-locking. Specifically the normally unnoted property of a cocking-lever shaft gear to be self-locking despite low frictional losses is very valuable in this case. In addition it produces no axial forces. Due to the central axis of the strain-wave gear being coaxial with the swivel axis of the mirror unit the small axial width of such a gear can be fully utilized and its internal region be used to accommodate the swivel axis.
(b) The construction of the strain-wave gear with a driving eccentric, an elastic annular gear and two coaxial power take-off members working together with the latter and having different numbers of teeth is particularly space-saving and low in friction. The latter also allows the use of a weaker and consequently smaller motor.
(c) The strain-wave gear is especially small and low in friction when the driving eccentric has an external toothed structure in drive engagement with a pinion of the motor. Drive then ensues to a certain extent from the side which further reduces the overall height and allows good dissipation of gearing forces. Moreover, in this way the motor can be arranged apart from the swivel axis and with its power take-off pinion very low which is further to the benefit of the fitting dimensions.
(d) As a result that of the two power take-off members coaxial with one another and with the swivel axis one has a drive connection to the base and one to the mirror unit the two power take-off members are arranged directly coaxially with the parts to which they are connected, the base and mirror unit, without an further transmission-members being required. In this way the overall shape of the drive unit is ideally adapted to the fitting situation.
In a preferred specific embodiment the driving eccentric of the strain-wave gear is arranged inside and the two power take-off members are arranged outside the elastic annular gear and one of the two power take-off members is part of the gear housing and the other power take-off member has a drive connection to the part which is movable relative to the gear housing (claim 2). The movable part can be both the base as well as the mirror unit. In both cases due to the power take-off on the outside power transmission is again possible without any intermediate members. The drive from the inside results in a particularly good arrangement of the elastic annular gear which increases the power density.
A particularly light and space-saving design is achieved when the driving eccentric possesses at least two sliding blocks arranged at the same angular spacing from one another which slide on the inside of the elastic annular gear (claim 3). Between these the driving eccentric has support webs (claim 4) which prevent sagging of the elastic annular gear between the sliding blocks which can cause poor engagement of the teeth.
Advantageously, the driving eccentric has a central opening for the passage of the pivot pin and runs substantially in the plane of its outer toothed structure in bearings of which one is seated in one power take-off member and one in the other power take-off member or in parts rigidly connected thereto (claim 5). The cocking-lever shaft gear is thus built around the axis about which the mirror unit is pivoted. The driving eccentric is precisely mounted and centered which makes a considerable contribution to clean engagement and low wear of the gear parts so that they can even be made of plastic.
In a refinement of the invention the drive connection between the pinion of the motor and the outer toothed structure of the driving eccentric can be established via at least one spur wheel stage (claim 6). Apart from the greater transmission ratio made possible in this way this allows still greater freedom of design for the outer shape of the pivot drive unit because the motor can be arranged further from the-swivel axis.
In a preferred specific embodiment the pivot drive unit is accommodated in the mirror unit and the drive member not connected to the housing has a drive connection to a hollow axle connected in non-slipping manner to the base (claim 7). The attachment of the pivot drive unit in the moving part in which the spatial conditions are a little more favorable than in the base does not give rise to further expense since the leads for displacing the mirror are also led through the hollow axle.
The small axial height of the gear and the motor arranged apart allow enough space for a spring-loaded torque limiting coupling arranged between the power take-off member and the hollow axle, this being arranged on one side of the housing and the spring on the other side of the housing (claim 8). This affords an ideal arrangement with minimum requirement for space and there is even still space for a thrust bearing between the two power take-off members (claim 9) which further reduces frictional losses and wear.